Proprioception refers to the ability to know where a body part is located in space and to recognize movements of body parts (such as fingers and toes, feet and hands, legs and arms). Kinesthesia is a related term, and refers to the sensation by which position, weight, muscle tension and movement are perceived. In some of the medical literature, proprioception refers to the conscious and unconscious appreciation of joint position, while kinesthesia refers to the sensation of joint velocity and acceleration. Proprioception is often used interchangeably with kinesthesia, and herein as well, the terms will be used interchangeably. (Throughout the specification and claims, the term “proprioception” will be used to encompass proprioception, kinesthesia, core stability and the like.)
The neuromuscular control system of the body integrates peripheral sensations relative to joint loads and processes these signals into coordinated motor responses. This muscle activity serves to protect joint structures from excessive strain.
Certain mechanoreceptors are present throughout the soft tissues of the musculoskeletal system which interact with the central nervous system and coordinate body movements, postural alignment, and balance. Mechanoreceptors are located in the muscles, tendons, ligaments, joint capsules and the skin. These nerve fibers provide information to the brain regarding the status and function of the musculoskeletal system. The mechanoreceptors send electrical signals along peripheral nerves to the spinal cord. The electrical signals travel via the spinal cord to the brain where the signals are interpreted to recognize movements of body parts, muscle tension, movement and the like.
Some examples of mechanoreceptors for controlling the muscular system include muscle spindles. Muscle spindles are found interspersed within the contractile fibers of skeletal muscles, with the highest concentration in the central portion of each muscle. Muscle spindle fibers respond to changes in the length of muscles. These nerve endings provide the central nervous system information used to maintain muscle tone and the correct muscle tension on opposite sides of each joint.
Fibrous tissues that surround and protect most joints generally contain a variety of sensory nerve endings for proprioception and kinesthesia. The input from these sensory nerve endings provides the central nervous system information regarding the location, stretch, compression, tension, acceleration, and rotation of the joint.
The foot is the anatomical region that contains the second largest number of proprioceptive or kinesthetic sensory receptors in the body (the spine has the most).
Proprioceptive and kinesthetic exercises and exercise devices are well known for improving agility, balance and coordination, and for rehabilitation of persons whose proprioceptive ability has been impaired, such as after accidents or illness. One such class of exercise devices includes tilt boards, wherein a patient stands on a board or similar platform that has a ball mounted underneath. The board does not lie horizontal due to the presence of the ball, and this challenges the ability of the patient to balance and perform maneuvers on the platform. Repeated exercises on the tilt board may be used to develop or rehabilitate the proprioception and neuromuscular control of the patient, as well as strengthen muscles, tendons and connective tissues in the foot area.
Other known proprioceptive and kinesthetic exercise devices include a shoe with a single ball mounted underneath the sole of the shoe. The shoe with the ball is used similar to the tilt board. Another kind of shoe has a rod mounted underneath the sole of the shoe, used for strengthening dorsiflexor muscles.
Yet another proprioceptive and kinesthetic exercise device is described in U.S. Pat. No. 6,283,897 to Patton. This device consists of one or more pegs protruding upwards from a baseboard. The pegs have a rounded top and sit in concave depressions (divots) in the bottom of an overshoe shaped like a sandal. Specifically, the bottom of the shoe's sole has three concave, hemisphere-shaped divots, with one located within the heel portion, one directly underneath the ball of the foot, and one located in the center. Elastomeric bands may support the user's foot as the user turns his foot and/or hips to develop the strength, range of motion, and proprioception of the ankle and hips.